1. Field of the Invention
The present invention relates to a device for assisting identification of system events, such as intermittent faults. More specifically, the present invention relates to a time stress measurement device for time-tagging system events and associated environmental stresses applied to the system, for future use in identifying, understanding, and correcting intermittent system failures, and further for testing the system to determine if it is operating properly.
2. Description of the Related Art
Both industry and military organizations have examined procedures for streamlining maintenance of electronic and mechanical systems by reducing or removing intermediate maintenance, and by automating higher level depot maintenance. At present, fielded systems typically require several levels of maintenance support. These levels may include: (1) Organizational Maintenance, where system Built-in Test (BIT) and/or support equipment isolates faults to a single Line Replaceable Unit (LRU); (2) Intermediate Maintenance, where automatic or semi-automatic test equipment is used to isolate LRUs to a specific Shop Replaceable Unit (SRU); and (3) the Depot, where test equipment is used to isolate faults down to the component level.
Attempts to reduce Intermediate level maintenance have been hindered by three obstacles regularly experienced by maintenance personnel at all levels. These obstacles are typically known by their colloquial expressions as (1) fault isolation ambiguity, (2) Cannot Duplicate (CNDs), and (3) Re-Test OKs (ReTOKs). Fault isolation ambiguity is prevalent in systems where functional partitioning prevents BIT from isolating a failure to a single LRU or system interconnections. CNDs are system hard failures or intermittent failures which are detected by system users during system operations, but which cannot subsequently be duplicated (and hence not corrected) by maintenance personnel. ReTOKs reflect a maintenance quandary where a failure is detected by the system users and the Organizational maintenance personnel, resulting in an affected LRU being removed from the system. Subsequent testing in a depot facility, however, fails to detect any performance degradation. Having no apparent identifiable failure, the LRU is considered ReTOKed, and is returned to service.
In years past, several organizations using electronic aircraft systems have attempted to reduce Intermediate Maintenance support. To do so required Organization-level maintenance personnel to achieve an extremely high level of isolating faults detected by system-operating personnel. The level of fault detection/fault isolation achieved, however, was inadequate.
Existing systems lack the ability to detect an event, such as a fault, and record the time the fault is detected, while simultaneously recording the corresponding environmental data, e.g., temperature, shock, vibration, voltage, transients, analog and digital test points, and the like, which might either have caused the fault or contributed to the fault, or at least could provide maintenance personnel sufficient data to analyze the fault. Existing systems also lack the ability to send a test signal to the host system, determine whether the host system is operating properly, and record that test data.